As a power source for a vehicle such as an electric car, an electric motorcycle, or a power-assisted bicycle or as a power source for use in a house or a building, a battery module or a battery pack incorporating a secondary battery is available, and various types of secondary batteries can be used in the battery module or battery pack. Among the various types, a lithium ion battery excellent in both mass and volume energy densities and providing high voltage per unit battery is preferably used.
The lithium ion battery includes a wound type obtained by winding, in a roll shape, a stack of strip shaped positive and negative electrodes through a separator and a stacked type obtained by stacking flat plate-positive and negative electrodes through a separator. The lithium ion battery generally has a columnar or a flat shape as a whole.
Among them, a flat-shaped lithium ion battery obtained by packaging a battery element with a film-like member has a substantially rectangular shape to be tightly housed in a device, and has a light weight. Thus, with such a flat-shaped lithium ion battery, it is possible to realize a device having high volume energy density or a high mass energy density. In particular, the light weight property is significant for a power source battery for a power motor for, e.g., a vehicle.
A film-covered battery disclosed in Patent Document 1 is lower in strength against impact than a battery housed in a casing such as an aluminum can having a large thickness. Therefore, a frame member in which an opening is formed at a position corresponding to a power generation element of the film-covered battery is disposed so as to retain a heat-welded portion at a periphery of a covering material. Further, as another structure for supporting a battery with a frame, Patent Document 2 proposes a structure in which an elastic pressurizing member is provided at a part of the frame so as to surely bring a heat radiating plate provided in the battery into tight contact with the battery.